The present invention relates to an apparatus and to a process for the production of bremsstrahlung (braking radiation) from acceleration electrons.
The present invention relates to all fields requiring the production of bremsstrahlung, such as .gamma. or X-radiation. The invention more particularly applies to the field of physics, biological and medical research, the detection of faults in materials and the irradiation of food or industrial products.
FIG. 1 diagrammatically shows in section the structure of a betatron or electron accelerator. It comprises a ferromagnetic part 1 having two separate facing portions 3, 4 corresponding to the North and South poles of the part, a solenoid 5 in the centre of the part connecting the two portions 3 and 4 and a toroidal cavity 7 under vacuum in the median plane of the part. This cavity contains the electrons conventionally produced from an electron source, such as a filament or a plasma introduced into the cavity. There is a mgnetic field B perpendicular to the median plane between the two separate portions of the part.
The electrons present in the cavity, under the effect of the magnetic field B, are rotated in accordance with a circular trajectory or path 9 of radius R in a plane perpendicular to the magnetic field direction. This radius R is a function of the electron velocity V and the intensity of the magnetic induction B, in accordance with the euation R=mv/(eB), in which e represents the charge of the electrons and m their mass.
In order to accelerate the electrons, which initially have a low velocity, the magnetic induction intensity is increased. Thus, when the magnetic induction beam increases, the radius R of the path remains fixed and the velocity v of the electrons increases ##EQU1##
The rise in the magnetic induction is dependent on the voltage applied to the terminals of solenoid 5, the higher the voltage the higher the induced field.
The electrons accelerated in a betatron are particularly used for the study of matter. For focusing the beam of electrons, a toroidal coil to whose terminals a voltage is applied, can be introduced into the cavity in such a way that the electron beam traverses said coil. This type of betatron is generally called a "modified betatron" and is e.g. described by N Rostoker, of the University of California in the publication "Comments on plasm physics", 1980, vol 6, No. 2, pp 91-100.
Due to the presence of the magnetic field, the accelerated electron beam cannot be easily extracted from the betatron for use for producing radiation by the interaction of these electrons with a target.
In known manner, a target is directly introduced into the cavity containing the electrons in order to produce bremsstrahlung in the betatron. As bremsstrahlung is not sensitive to the magnetic field induced in the cavity, the latter can consequently escape from the betatron and be used.
FIG. 2 diagrammatically shows the interaction of electrons with a target placed on the circular path of these electrons. Thus, FIG. 2 shows the circular path 10 of electrons e rotated by a magnetic field B perpendicular to the plane of said path. A target 11 is placed on the path of the electrons to interact therewith.
The electron-target interaction leads to the emission of bremsstrahlung 12, which is substantially tangential to the circular path of the electrons. The bremsstrahlung is insensitive to the presence of the magnetic field, so that it not made to travel on a circular path.
An apparatus using a target placed on the circular path of accelerated electrons for producing bremsstrahlung is e.g. described in U.S. Pat. No. 2,335,014.
In an apparatus of this type, the target used and which rotates in a plane perpendicular to that of the electron path, is entirely disposed within the cavity containing the accelerated electrons. Thus, the target has a limited length and the latter is in particular less than the diameter of the path of the electrons.
A target of this type does not make it possible to produce high power radiation, i.e. of a few kW, as is more particularly used in the industrial irradiation field.